In recent years, communication between a terminal and a server or terminals connected through a public line network, has provided various services. For example, it is known that a remote support service for users who operate a personal computer and electronic equipment is provided via a network such as a public line network. Such a remote support service allows customer support staff to access users' personal computers and electronic equipment directly so as to understand the situation or the problem in the computers and electronic equipment. (For example, see non-patent document 1.)
In such a remote support service, to communicate between a user terminal receiving a support service and a support terminal providing a support service through a public line network, devices having a global address should be required. In other words, the user terminal and the support terminal have only their respective private address assigned to a local area network (hereinafter referred to as “LAN”), so that they cannot communicate with each other through a public line network unless a connection server or a router having a global address mediate their communication. For example, a support terminal is connected with a connection server through a LAN, a user terminal is connected with a router through a LAN, and the connection server and the router are connected through a public line network. In this case, the support terminal and the user terminal can communicate with each other.
Then, the user terminal receiving a support service sends an access request to the support terminal so as to start communication between the support terminal and the user terminal through the connection server and the router.    Non-patent document 1: Remote Support Service. [online].NIPPON TELEGRAPH AND TELEPHONE EAST CORPORATION, [retrieval on Jul. 22, 2009].